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United States Patent |
5,279,172
|
Genise
|
January 18, 1994
|
Four position fluid-actuated piston arrangement
Abstract
A fluid pressure-operated shift actuator (11) is provided of the type
defining a series of fluid pressure chambers (69, 71, 91, and 95). The
actuator is operable to move a shift finger (19) to any one of four shift
rails (1,2,3,4) by actuating various combinations of solenoids (29,31,33).
One of the fluid pressure chambers (95) provides a constant bias of the
shift finger (19) toward the first shift rail (1). Actuation of the second
and third pressure chambers (71,91) results in selection of the third
shift rail, because pressurization of the third pressure chamber (91)
limits the rightward movement of the crank arrangement (37) which directly
controls position of the shift finger (19).
Inventors:
|
Genise; Thomas A. (Dearborne, MI)
|
Assignee:
|
Eaton Corporation (Cleveland, OH)
|
Appl. No.:
|
965680 |
Filed:
|
October 22, 1992 |
Current U.S. Class: |
74/335 |
Intern'l Class: |
F16H 059/04 |
Field of Search: |
74/335,346,364
|
References Cited
U.S. Patent Documents
2157592 | May., 1939 | Casler | 74/346.
|
2297026 | Sep., 1942 | Sanford et al. | 74/346.
|
2432712 | Dec., 1947 | Bachman et al. | 74/346.
|
2931237 | May., 1960 | Backus | 74/335.
|
2974766 | Mar., 1961 | Perkins et al. | 74/364.
|
3058364 | Oct., 1962 | Alfieri | 74/346.
|
4718307 | Jan., 1988 | Yabe et al. | 74/335.
|
4899607 | Feb., 1990 | Stainton | 74/364.
|
4911031 | Mar., 1990 | Yoshimura et al. | 74/335.
|
Foreign Patent Documents |
606421 | Dec., 1934 | DE2 | 74/346.
|
Primary Examiner: Wright; Dirk
Attorney, Agent or Firm: Kasper; L. J.
Claims
I claim:
1. A fluid pressure operated shift-actuator for use with a mechanical
transmission having a plurality of axially movable shift rails, said
shift-actuator being operable to move a shift finger in the X--X direction
and being adapted to engage a desired one of said shift rails; said
shift-actuator including housing means defining first and second bores
disposed on one side of said shift finger, and a third bore disposed on
the other side of said shift finger; a first piston disposed in said first
bore and cooperating therewith to define a first fluid pressure chamber in
communication with a source of fluid pressure by means of a first fluid
control, a second piston disposed in said second bore and cooperating
therewith to define a second fluid pressure chamber in communication with
said source by means of a second fluid control, and a third piston
disposed in said third bore and cooperating therewith to define a third
fluid pressure chamber in communication with said source by means of a
third fluid control; said plurality of shift rails including first,
second, third, and fourth shift rails, and said second and third pistons
being operably associated with said shift finger whereby fluid pressure in
said second fluid pressure chamber biases said shift finger toward a
position adapted to engage said fourth shift rail and fluid pressure in
said third fluid pressure chamber biases said shift finger toward a
position adapted to engage said first shift rail; means providing a
constant bias of said shift finger toward a position adapted for
engagement with said first shift rail in the absence of pressure in said
first, second, and third fluid pressure chambers; said housing means and
said first and second pistons being configured to move said shift finger
to a position adapted for engagement with said second shift rail in
response to pressure in said first fluid pressure chamber; said housing
means and said second and third pistons being configured to move said
shift finger to a position adapted for engagement with said third shift
rail in response to pressure in said second and third fluid pressure
chambers, and to move said shift finger to a position adapted for
engagement with said fourth shift rail in response to pressure only in
said second fluid pressure chamber.
2. A fluid pressure operated shift-actuator as claimed in claim 1,
characterized by said means providing said constant bias comprises said
housing means and one of said second and third pistons defining a fourth
fluid pressure chamber in continuous fluid communication with said source
of fluid pressure; pressure in said fourth fluid pressure chamber exerting
a constant biasing force on said shift finger which is less than the
biasing force exerted by pressure in said second fluid pressure chamber.
3. A fluid pressure operated shift-actuator as claimed in claim 2,
characterized by said first fluid pressure chamber having an effective
area greater than an effective area of said fourth fluid pressure chamber;
pressure in said first fluid pressure chamber inserting a biasing force on
said shift finger which is greater than the constant biasing force exerted
by pressure in said fourth fluid pressure chamber.
4. A fluid pressure operated shift-actuator as claimed in claim 3,
characterized by said second fluid pressure chamber having an effective
area greater than an effective area of said third fluid pressure chamber;
but said effective area being less than the sum of the effective area of
said third fluid pressure chamber plus an effective area of said fourth
fluid pressure chamber.
5. A fluid pressure operated shift-actuator as claimed in claim 1,
characterized by said second and third pistons being operably associated
with said shift finger by means of a generally U-shaped crank member
having first and second upstanding portions disposed on said one side and
said other side, respectively, of said shift finger and defining an
opening receiving said shift finger; said second piston being in
engagement with said first upstanding portion and said third piston being
in engagement with said second upstanding portion.
6. A fluid pressure operated shift-actuator for use with a mechanical
transmission having a plurality of axially movable shift rails, said
shift-actuator being operable to move a shift finger in the X--X direction
to be adapted to engage a desired one of said shift rails; said
shift-actuator including housing means defining first and second bores
disposed on one side of said shift finger, and a third bore disposed on
the other side of said shift finger; a first piston disposed in said first
bore and cooperating therewith to define a first fluid pressure chamber in
communication with a source of fluid pressure by means of a first fluid
control, a second piston disposed in said second bore and cooperating
therewith to define a second fluid pressure chamber in communication with
said source by means of a second fluid control, and a third piston
disposed in said third bore and cooperating therewith to define a third
fluid pressure chamber in communication with said source by means of a
third fluid control; said plurality of shift rails including first,
second, third, and fourth shift rails, and said second and third pistons
being operably associated with said shift finger whereby fluid pressure in
said second fluid pressure chamber biases said shift finger toward a
position adapted to engage said fourth shift rail and fluid pressure in
said third fluid pressure chamber biases said shift finger toward a
position adapted to engage said first shift rail; one of said second and
third pistons defining a fourth fluid pressure chamber in continuous fluid
communication with said source of fluid pressure to provide a constant
bias of said shift finger toward a position adapted for engagement with
said first shift rail in the absence of fluid pressure in said first,
second, and third fluid pressure chambers; said first, second, third, and
fourth fluid pressure chambers having effective areas, respectively; said
effective area being greater than said effective area, and greater than
said effective area, but, less than the sum of said effective area plus
said effective area.
7. A fluid pressure operated shift-actuator as claimed in claim 6,
characterized by said effective area of said first fluid pressure chamber
being greater than said effective area of said second fluid pressure
chamber, and greater than said effective area of said fourth fluid
pressure chamber.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a pressurized fluid operated shifting
mechanism for cooperation with a shift bar housing assembly for
selectively shifting a change-gear mechanical transmission. More
particularly, the present invention relates to such a fluid operated
shifting mechanism of the "X--Y" type, and will be described in connection
therewith.
Shift bar housing assemblies for change-gear mechanical transmissions
typically comprise a plurality of generally parallel, independently
axially movable shift bars or shift rails, each carrying a shift fork
fixed thereto. Each shift bar or shift rail may be selected and moved
axially to effect engagement/disengagement of a particular gear ratio.
Such assemblies are well known in the prior art and may be better
understood by reference to U.S. Pat. Nos. 4,455,883; 4,575,029; and
4,584,895, all of which are incorporated herein by reference.
Such shift bar housings may be manually controlled by the vehicle operator,
by means of a shift lever. More recently, it is becoming increasingly
popular to utilize automatically controlled pressurized fluid actuating
shift-actuators with such shift bar housings. In a pressurized fluid
operated shift-actuator, a shift finger is automatically moved in the X--X
(rail selection) direction, in response to actuation of one fluid pressure
device, then the shift finger is automatically moved in the Y--Y (gear
engagement/disengagement) direction in response to actuation of another
fluid operated device.
Shift bar housing assemblies utilizing pressure operated shift-actuators to
control each shift rail in an automatic or semi-automatic mechanical
transmission are known in the prior art, as may be better understood by
reference to U.S. Pat. Nos. 4,445,393, 4,722, 237, and 4,928,544 all of
which are incorporated herein by reference.
The prior art fluid operated shift-actuators for providing automatic and/or
semi-automatic rail selection of change gear mechanical transmissions were
generally satisfactory for use with transmissions including only three
shift rails (i.e., five forward speeds plus reverse). However, it has
become quite desirable to be able to achieve automatic and/or
semi-automatic rail selection and shifting of transmissions having four
shift rails (i.e., seven forward speeds plus reverse). See for example
U.S. Pat. No. 4,388,838, assigned to the assignee of the present invention
and incorporated herein by reference. For such transmissions, the known
fluid pressure operated shift-actuator for moving the shift finger in the
X--X (rail selection) direction, is not commercially available, and is not
known in the prior art.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an
improved fluid operated shift-actuator for a mechanical transmission which
is capable of selecting from among four different shift rails, while
utilizing only a single source of pressurized fluid, and only three
pistons and solenoid valves.
It is a more specific object of the present invention to provide such an
improved shift-actuator in which two of the piston and solenoid valves are
disposed on one axial side of the shift finger, while the third piston and
solenoid valve are located on the other axial side of the shift finger,
thus making it possible to avoid the use of three progressively larger
fluid pressure pistons in sequence, on one axial side of the shift finger.
The above and other objects of the invention are accomplished by the
provision of a fluid pressure-operated shift actuator for use with a
mechanical transmission having a plurality of axially movable shift rails,
the shift actuator being operable to move a shift finger in the X--X
direction to engage a desired one of the shift rails. The shift actuator
includes housing means including first and second bores disposed on one
side of the shift finger, and a third bore disposed on the other side of
the shift finger. A first piston is disposed in the first bore, and
cooperates therewith to define a first fluid pressure chamber in
communication with a source of fluid pressure by means of a first fluid
control. A second piston is disposed in the second bore and cooperates
therewith to define a second fluid chamber in communication with the
source by means of a second fluid control. A third piston is disposed in
the third bore, and cooperates therewith to define a third fluid pressure
chamber in communication with the source by means of a third fluid
control. The plurality of shift rails includes first, second, third, and
fourth shift rails. The second and third pistons are operably associated
with the shift finger, whereby fluid pressure in the second fluid pressure
chamber biases the shift finger toward the fourth shift rail, and fluid
pressure in the third fluid pressure chamber biases the shift finger
towards the first shift rail. Means are included to provide a constant
bias of the shift finger toward engagement with the first shift rail, in
the absence of pressure in the first, second, and third fluid pressure
chambers. The housing means and the first and second pistons are
configured to move the shift finger to engagement with the second shift
rail in response to pressure in the first pressure chamber. The housing
and the second and third pistons are configured to move the shift finger
to engagement with the third shift rail in response to pressure in the
second and third pressure chambers, and to move the shift finger to
engagement with the fourth shift rail in response to pressure only in the
second fluid pressure chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top plan view, partly broken away, of an X--Y shifting
mechanism of the type with which the present invention may be utilized.
FIG. 2 is a transverse cross-section, taken on line 2--2 of FIG. 1, but on
a somewhat larger scale, illustrating an X--X actuator made in accordance
with the present invention, shown in a position selecting the second shift
rail.
FIG. 2A is a schematic representation of the shift pattern highlighted to
correspond to the actuator position shown in FIG. 2.
FIG. 2B is an enlarged fragmentary, axial cross-section similar to FIG. 2,
illustrating a particular detail of the present invention.
FIG. 3 is a transverse cross-section, similar to FIG. 2, and on the same
scale, but with the actuator selecting the third rail.
FIG. 3A is a schematic representation of the shift pattern, highlighted to
correspond with the actuator position shown in FIG. 3.
FIG. 4 is an axial cross-section, similar to FIGS. 2 and 3, and on the same
scale, illustrating the actuator selecting the fourth shift rail.
FIG. 4A is a schematic representation of the shift pattern, highlighted to
correspond to the actuator position shown in FIG. 4.
FIG. 5 is a truth table illustrating the operation of the present invention
.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, which are not intended to limit the
invention, FIG. 1 illustrates a top plan view of a fluid operated shift
actuator, generally designated 11, of the type with which the present
invention may be utilized. The shift actuator would typically be used with
a change-gear heavy duty truck mechanical transmission, of the general
type now well known in the art, and illustrated in U.S. Pat. No.
3,105,395, incorporated herein by reference.
Such transmissions typically include a shift bar housing assembly of the
type shown in above-incorporated U.S. Pat. No. 4,928,544. Such shift-bar
housing assemblies (not shown herein) typically comprise a plurality of
shift rails movable axially (from left to right, or right to left in FIG.
1, or up and down in the shift pattern of FIG. 2A), each of which carries
a shift fork fixed thereto for axial movement therewith, as is well known
to those skilled in the art. Shifting of such transmissions is
accomplished by selecting a shift rail, by moving an engagement member
such as a shift finger along the axis X--X (up and down in FIG. 1, or from
left to right, or right to left in FIG. 2A) into alignment with a shift
block carried by the selected shift rail. The actual shifting is then
accomplished by causing axial movement of the selected shift rail, by
axially moving the shift finger to apply an axial force in the direction
of the axis Y--Y. Therefore, the fluid operated shift actuator illustrated
herein is typically referred to as X--Y type of shift actuator, because it
is capable of moving a shift finger in both the X--X direction and the
Y--Y direction. It should be clearly understood, however, that the present
invention is not specifically limited to use in an X--Y type shift
actuator, but instead, may be used in any type of fluid operated shift
actuator in which it is required to be able to move the shift finger to
any one of four different shift rails.
The X--Y shift actuator 11 is enclosed within a housing 13 having a
mounting plate portion 15 defining bolt bores 17 in a pattern allowing the
actuator 11 to be mounted to the upper opening of a transmission shift bar
housing assembly. As may best be seen in FIG. 2, a shift finger 19 extends
downwardly from the housing 13 for interaction with the shift rails (not
shown herein). This will be described subsequently.
The housing 13 includes a housing portion 21, which encloses a
piston-cylinder assembly, generally designated 23, for moving the shift
finger 19 transversely in the X--X direction (see FIG. 2). The housing 13
also includes a housing portion 25 which encloses a piston-cylinder
assembly, generally designated 27, which is also involved in moving the
shift finger 19 in the X--X direction (again see FIG. 2).
Associated with the housing portion 21 and the piston-cylinder assembly 23
is a pair of three-way, two-position solenoid valves 29 and 31. Similarly,
associated with the housing portion 25 and the piston-cylinder assembly 27
is another three-way, two-position solenoid valve 33. The solenoid valves
29, 31, and 33 may be of a standard type having a first port connected to
a common manifold of pressurized fluid, a second port connected to a
common exhaust manifold, and a third port connected to its respective
individual pressure chamber, to be controlled by the particular solenoid
valve. The valves are normally in the chamber-exhaust position, and by
actuation of the solenoids, are movable to the chamber-pressurization
position, as will be described in greater detail subsequently.
Referring again only to FIG. 1, the shift actuator 11 includes a Y--Y shift
actuator, generally designated 35, which is generally well-known in the
art, forms no part of the present invention, and therefore will not be
described or even illustrated herein. The Y--Y shift actuator may be made
in accordance with the teachings of co-pending application U.S. Ser. No.
919,349, filed Jul. 23, 1992 for a "DUAL FORCE FLUID ACTUATED SHIFT
DEVICE", in the name of Thomas A. Genise, the co-pending application being
assigned to the assignee of the present invention and incorporated herein
by reference.
Referring now primarily to FIG. 2, the X--X shift actuator will be
described in detail. The X--X shift actuator comprises primarily the
piston cylinder assembly 23, the piston cylinder assembly 27, and a crank
arrangement generally designated 37. The crank arrangement 37 includes a
generally U-shaped crank member 39, including upstanding portions 37a and
37b, which defines an opening 41 through which the shift finger 19 extends
downwardly for engagement with the appropriate one of the shift rails. For
purposes of simplicity, the shift rails, from left to right, bear the
reference numerals 1, 2, 3, and 4, and in accordance with conventional
nomenclature, will hereinafter be referred to as the first, second, third,
and fourth shift rails. The shift finger 19 comprises a lower extremity of
a shift finger carrier 43, which is in fixed, non-rotatable engagement by
means of a key 45, with a piston rod 47. As is well understood by those
skilled in the art, the piston rod 47 forms a primary element of the Y--Y
shift actuator 35, whereby, after the X--X shift actuator selects the
appropriate one of the shift rails 1, 2, 3, or 4, the Y--Y shift actuator
35 moves the piston rod 47 in the appropriate direction (to the left or
the right in FIG. 1; into or out of the plane of FIG. 2) to move the
selected shift rail in the appropriate direction (e.g., into gear
engagement). By way of example only, as may be seen in FIG. 2a, with the
shift finger 19 engaging the shift rail 2, actuation of the Y--Y shift
actuator 35 can achieve gear engagement to effect operation either in
fourth gear or in fifth gear.
Pivotal movement of the shift finger carrier 43 about the axis of the
piston rod 47 is accomplished by reciprocating movement of the crank
arrangement 37 (i.e., movement from left to right, or from right to left
in FIG. 2). Such movement of the crank arrangement 37 is accomplished by
appropriate pressurization of the piston-cylinder assemblies 23 and 27.
The piston-cylinder assembly 23 will now be described in some detail.
The housing portion 21 defines a stepped cylinder bore including a
relatively larger bore portion 49 and a relatively smaller bore portion
51. Disposed within the bore portion 49 is a larger piston 53, including a
rightwardly-extending portion 55, the purpose of which will be described
subsequently. Disposed within the smaller bore portion 51 is a smaller
piston 57, which defines a cylindrical, hollow portion 59, within which
the rightwardly-extending portion 55 is received. The smaller piston 57
includes a shaft portion 61, which is received in a bore defined by the
housing portion 21, the shaft portion 61 including a smaller diameter
terminal portion 63. The terminal portion 63 is received in a bore defined
by the U-shaped crank member 39, and is axially restrained relative to the
crank member 39 by a set screw 65.
Disposed adjacent the left end of the housing portion 21 (in FIG. 2) is a
gasket member 67, and the gasket 67 cooperates with the larger bore
portion 49 and the larger piston 53 to define a first fluid pressure
chamber 69. The smaller bore portion 51 cooperates with the smaller piston
57 to define a second fluid pressure chamber 71. Fluid pressure in the
first and second fluid pressure chambers 69 and 71 is controlled by the
solenoid valves 29 and 31, respectively (see FIG. 1). Fluid pressure in
either of the chambers 69 or 71 will tend to move crank arrangement 37 to
the right in FIG. 2, i.e., toward a higher numbered shift rail.
Referring still primarily to FIG. 2, the piston-cylinder assembly 27
comprises the housing portion 25 defining a stepped bore including a
larger bore portion 73 and a relatively smaller bore portion 75. The right
end (in FIG. 2) of the larger bore portion 73 is closed by means of a
sealed plug 77, held in place by means of a snap ring 79. Disposed within
the larger bore portion 73 is a piston 81, which includes a
leftwardly-extending portion 83. Disposed within the smaller bore portion
75 is a shaft portion 85, including a smaller diameter terminal portion 87
which is received in a bore defined by the U-shaped crank member 39, in
the same manner as previously described, and is restrained axially
relative thereto by means of another set screw 65. The shaft portion 85
defines a generally cylindrical, hollow portion 89, which receives the
leftwardly-extending portion 83 therein. It should be noted that each of
the portions 55 and 83 include a somewhat spherical portion which may be
received in a relatively close fit within the respective hollow portion 59
or 89, without affecting the alignment of the pistons 53 and 55, or the
piston 81 and shaft portion 85, in the event the respective bore portions
are not perfectly concentric.
The plug 77 cooperates with the larger bore portion 73 and the piston 81 to
define a third fluid pressure chamber 91, with the fluid pressure in the
chamber 91 being controlled by the solenoid valve 33. The smaller bore
portion 75 cooperates with the piston 81 and the shaft portion 85 to
define a vented chamber 93. By "vented" it is typically meant that the
chamber 93 is in permanent communication with a source of low pressure,
such as the atmosphere, although those skilled in the art will recognize
that the chamber 93 could also be connected to a constant source of
relatively low pressure, but which is at a higher pressure than
atmosphere. As will be apparent from FIG. 2, fluid pressure in the third
fluid pressure chamber 91 will exert a force on the piston 81 tending to
move the crank arrangement 37 to the left in FIG. 2, toward a lower
numbered shift rail, or at least resisting the tendency of the crank
arrangement 37 to move to the right in FIG. 2.
The housing portion 21 cooperates with the shaft portion 61 and the smaller
piston 57 to define a fourth fluid pressure chamber 95 which is in
continuous fluid communication with a source of fluid pressure, which is,
preferably, and for simplicity, the same source to which the solenoid
valves 29, 31, and 33 are connected. Fluid pressure in the fourth fluid
pressure chamber 95 exerts a biasing force on the smaller piston 57,
biasing it and the crank arrangement 37 to the left in FIG. 2, toward
engagement with a lower numbered shift rail.
Operation
Referring now primarily to FIGS. 2, 2A, and 5, the operation of the X--X
shift actuator of the present invention will be described. With all of the
solenoid valves 29, 31, and 33 unactuated, there is relatively low
(basically atmospheric) pressure in the first, second, and third fluid
pressure chambers 69, 71, and 91. Thus, in this condition, only the fourth
fluid pressure chamber 95 contains pressure, which biases both the smaller
piston 57 and the larger piston 53 to the left in FIG. 2 until the piston
53 engages the gasket 67. In the condition described, the crank
arrangement 37 is moved to the left from the position shown in FIG. 2 a
sufficient distance for the shift finger 19 to engage the shift rail 1,
such that the operator may then select either sixth gear or seventh gear.
Referring still to FIGS. 2, 2A, and 5, if the solenoid valve 29 is
actuated, with the solenoid valves 31 and 33 being unactuated, there is
pressure in the first fluid pressure chamber 69 and in the fourth fluid
pressure chamber 95, but substantially no pressure in the second and third
fluid pressure chambers 71 and 91. In the condition described, the piston
53 is biased to the right in FIG. 2 until it engages a shoulder 97 defined
at the intersection of the bore portions 49 and 51 (see FIG. 2B). With the
piston 53 biased to the position shown in FIG. 2, the
rightwardly-extending portion 55 engages the smaller piston 57, moving it
to the right in FIG. 2, overcoming the bias force of the pressure in the
fourth fluid pressure chamber 95. The crank arrangement 37 is thus moved
to the position shown in FIG. 2, moving the shift finger 19 into
engagement with the shift rail 2, such that the operator can then select
either fourth or fifth gear.
Although not an essential feature of the invention, in the X--X shift
actuator of the present invention, the first fluid pressure chamber 69 has
an effective area (i.e., transverse cross-sectional area, subjected to
fluid pressure) which is designated A1. The effective area A1 is merely
the area of the left end surface of the larger piston 53. The second fluid
pressure chamber 71 has an effective area designated A2, the effective
area A2 being the net area on the left end surface of the smaller piston
57. Preferably, the effective area A2 is less than the effective area A1.
The third fluid pressure chamber 91 has an effective area designated A3,
the effective area A3 being merely the area of the right end surface of
the piston 81. The effective area A3 is preferably less than A2, although
it can be larger than, or the same as, A2. The fourth fluid pressure
chamber 95 has an effective area designated A4, the effective area A4
being the area of the right end surface of the piston 57, minus the area
of the shaft portion 61. Preferably, the effective area A4 is less than
the effective area A3.
Referring now primarily to FIGS. 3, 3A, and 5, if the solenoid valve 29 is
de-actuated, and each of the solenoid valves 31 and 33 is actuated, the
larger piston 53 will be biased to the left in FIG. 3 by pressure in the
second fluid pressure chamber 71, with the piston 53 engaging the gasket
67. In this position, the first fluid pressure chamber 69 decreases to
almost zero volume. At the same time, the pressure in the second fluid
pressure chamber 71 biases the smaller piston 57 to the right in FIG. 3,
in opposition to the constant pressure in the fourth fluid pressure
chamber 95. There is also fluid pressure in the third fluid pressure
chamber 91, biasing the piston 81 against a shoulder 99 defined at the
intersection of the larger and smaller bore portions 73 and 75. In
accordance with one aspect of the present invention, the areas of the
various pistons and chambers are selected such that the area A2 of the
piston 57 is less than the sum of the effective area A3 of the piston 81
plus the effective area A4 of the chamber 95 (also acting on the piston
57). As a result, with both of the solenoid valves 31 and 33 actuated, as
shown in FIG. 5, the pressure in the second fluid pressure chamber 71
moves the crank arrangement 37 to the right in FIG. 3 until the shaft
portion 85 engages the end of the leftwardly-extending portion 83 (the
position shown in FIG. 3). Because of the fluid pressure in the third
fluid pressure chamber 91, and further because of the previously described
relationship of the effective areas A1, A2, A3, and A4, the biasing force
on the piston 57 is not sufficient to overcome the combined biasing forces
in the chambers 91 and 95, and the crank 37 stops at the position shown in
FIG. 3, with the shift finger 19 in engagement with the shift rail 3, from
where the operator can select either second gear or third gear.
Referring now primarily to FIGS. 4, 4A, and 5, there will be described a
condition in which the solenoid valves 29 and 33 are de-actuated, and only
the solenoid valve 31 is actuated. In that condition, the piston 53 is
again biased to the left in FIG. 4 by pressure in the second fluid
pressure chamber 71, with the pressure in the chamber 71 again biasing the
smaller piston to the right, in opposition to the biasing force of
pressure in the fourth fluid pressure chamber 95. The difference in this
condition, compared to the condition described in connection with FIG. 3,
is that with the solenoid valve 33 de-actuated, there is no substantial
fluid pressure in the third fluid pressure chamber 91. Therefore, as the
piston 57 moves to the position shown in FIG. 3, there is no longer
pressure in the chamber 91 to resist further rightward movement, and the
crank 37 and shaft portion 85 continue to move to the right, pushing the
piston 81 to the right, reducing the volume of the chamber 91, but at the
same time, increasing the volume of the vented chamber 93. As this occurs,
the shift finger 19 is moved further to the right, into engagement with
the shift rail 4, from where the operator can select either reverse speed
gear or first gear.
Thus, it may be seen that with the X--X shift actuator of the present
invention it is possible to select any one of four shift rails, utilizing
only three pistons and three solenoid valves. Furthermore, it is possible
to achieve the desired result without the additional complexity which
would result if all three of the pistons were aligned, in sequence, on the
same side of the shift finger. Such an arrangement would require a larger
and more complex piston-cylinder arrangement.
The invention has been described in great detail in the foregoing
specification, and it is believed that various alterations and
modifications of the invention will become apparent to those skilled in
the art from a reading and understanding of the specification. It is
intended that all such alterations and modifications are included in the
invention, insofar as they come within the scope of the appended claims.
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